vllm/docs/source/usage/multimodal_inputs.md

(multimodal-inputs)=

# Multimodal Inputs

This page teaches you how to pass multi-modal inputs to [multi-modal models](#supported-mm-models) in vLLM.

```{note}
We are actively iterating on multi-modal support. See [this RFC](https://github.com/vllm-project/vllm/issues/4194) for upcoming changes,
and [open an issue on GitHub](https://github.com/vllm-project/vllm/issues/new/choose) if you have any feedback or feature requests.
```

## Offline Inference

To input multi-modal data, follow this schema in {class}`vllm.inputs.PromptType`:

- `prompt`: The prompt should follow the format that is documented on HuggingFace.
- `multi_modal_data`: This is a dictionary that follows the schema defined in {class}`vllm.multimodal.MultiModalDataDict`.

### Image

You can pass a single image to the {code}`'image'` field of the multi-modal dictionary, as shown in the following examples:

```python
llm = LLM(model="llava-hf/llava-1.5-7b-hf")

# Refer to the HuggingFace repo for the correct format to use
prompt = "USER: <image>\nWhat is the content of this image?\nASSISTANT:"

# Load the image using PIL.Image
image = PIL.Image.open(...)

# Single prompt inference
outputs = llm.generate({
    "prompt": prompt,
    "multi_modal_data": {"image": image},
})

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)

# Batch inference
image_1 = PIL.Image.open(...)
image_2 = PIL.Image.open(...)
outputs = llm.generate(
    [
        {
            "prompt": "USER: <image>\nWhat is the content of this image?\nASSISTANT:",
            "multi_modal_data": {"image": image_1},
        },
        {
            "prompt": "USER: <image>\nWhat's the color of this image?\nASSISTANT:",
            "multi_modal_data": {"image": image_2},
        }
    ]
)

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)
```

A code example can be found in [examples/offline_inference_vision_language.py](https://github.com/vllm-project/vllm/blob/main/examples/offline_inference_vision_language.py).

To substitute multiple images inside the same text prompt, you can pass in a list of images instead:

```python
llm = LLM(
    model="microsoft/Phi-3.5-vision-instruct",
    trust_remote_code=True,  # Required to load Phi-3.5-vision
    max_model_len=4096,  # Otherwise, it may not fit in smaller GPUs
    limit_mm_per_prompt={"image": 2},  # The maximum number to accept
)

# Refer to the HuggingFace repo for the correct format to use
prompt = "<|user|>\n<|image_1|>\n<|image_2|>\nWhat is the content of each image?<|end|>\n<|assistant|>\n"

# Load the images using PIL.Image
image1 = PIL.Image.open(...)
image2 = PIL.Image.open(...)

outputs = llm.generate({
    "prompt": prompt,
    "multi_modal_data": {
        "image": [image1, image2]
    },
})

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)
```

A code example can be found in [examples/offline_inference_vision_language_multi_image.py](https://github.com/vllm-project/vllm/blob/main/examples/offline_inference_vision_language_multi_image.py).

Multi-image input can be extended to perform video captioning. We show this with [Qwen2-VL](https://huggingface.co/Qwen/Qwen2-VL-2B-Instruct) as it supports videos:

```python
# Specify the maximum number of frames per video to be 4. This can be changed.
llm = LLM("Qwen/Qwen2-VL-2B-Instruct", limit_mm_per_prompt={"image": 4})

# Create the request payload.
video_frames = ... # load your video making sure it only has the number of frames specified earlier.
message = {
    "role": "user",
    "content": [
        {"type": "text", "text": "Describe this set of frames. Consider the frames to be a part of the same video."},
    ],
}
for i in range(len(video_frames)):
    base64_image = encode_image(video_frames[i]) # base64 encoding.
    new_image = {"type": "image_url", "image_url": {"url": f"data:image/jpeg;base64,{base64_image}"}}
    message["content"].append(new_image)

# Perform inference and log output.
outputs = llm.chat([message])

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)
```

### Video

You can pass a list of NumPy arrays directly to the {code}`'video'` field of the multi-modal dictionary
instead of using multi-image input.

Please refer to [examples/offline_inference_vision_language.py](https://github.com/vllm-project/vllm/blob/main/examples/offline_inference_vision_language.py) for more details.

### Audio

You can pass a tuple {code}`(array, sampling_rate)` to the {code}`'audio'` field of the multi-modal dictionary.

Please refer to [examples/offline_inference_audio_language.py](https://github.com/vllm-project/vllm/blob/main/examples/offline_inference_audio_language.py) for more details.

### Embedding

To input pre-computed embeddings belonging to a data type (i.e. image, video, or audio) directly to the language model,
pass a tensor of shape {code}`(num_items, feature_size, hidden_size of LM)` to the corresponding field of the multi-modal dictionary.

```python
# Inference with image embeddings as input
llm = LLM(model="llava-hf/llava-1.5-7b-hf")

# Refer to the HuggingFace repo for the correct format to use
prompt = "USER: <image>\nWhat is the content of this image?\nASSISTANT:"

# Embeddings for single image
# torch.Tensor of shape (1, image_feature_size, hidden_size of LM)
image_embeds = torch.load(...)

outputs = llm.generate({
    "prompt": prompt,
    "multi_modal_data": {"image": image_embeds},
})

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)
```

For Qwen2-VL and MiniCPM-V, we accept additional parameters alongside the embeddings:

```python
# Construct the prompt based on your model
prompt = ...

# Embeddings for multiple images
# torch.Tensor of shape (num_images, image_feature_size, hidden_size of LM)
image_embeds = torch.load(...)

# Qwen2-VL
llm = LLM("Qwen/Qwen2-VL-2B-Instruct", limit_mm_per_prompt={"image": 4})
mm_data = {
    "image": {
        "image_embeds": image_embeds,
        # image_grid_thw is needed to calculate positional encoding.
        "image_grid_thw": torch.load(...),  # torch.Tensor of shape (1, 3),
    }
}

# MiniCPM-V
llm = LLM("openbmb/MiniCPM-V-2_6", trust_remote_code=True, limit_mm_per_prompt={"image": 4})
mm_data = {
    "image": {
        "image_embeds": image_embeds,
        # image_size_list is needed to calculate details of the sliced image.
        "image_size_list": [image.size for image in images],  # list of image sizes
    }
}

outputs = llm.generate({
    "prompt": prompt,
    "multi_modal_data": mm_data,
})

for o in outputs:
    generated_text = o.outputs[0].text
    print(generated_text)
```

## Online Inference

Our OpenAI-compatible server accepts multi-modal data via the [Chat Completions API](https://platform.openai.com/docs/api-reference/chat).

```{important}
A chat template is **required** to use Chat Completions API.

Although most models come with a chat template, for others you have to define one yourself.
The chat template can be inferred based on the documentation on the model's HuggingFace repo.
For example, LLaVA-1.5 (`llava-hf/llava-1.5-7b-hf`) requires a chat template that can be found [here](https://github.com/vllm-project/vllm/blob/main/examples/template_llava.jinja).
```

### Image

Image input is supported according to [OpenAI Vision API](https://platform.openai.com/docs/guides/vision).
Here is a simple example using Phi-3.5-Vision.

First, launch the OpenAI-compatible server:

```bash
vllm serve microsoft/Phi-3.5-vision-instruct --task generate \
  --trust-remote-code --max-model-len 4096 --limit-mm-per-prompt image=2
```

Then, you can use the OpenAI client as follows:

```python
from openai import OpenAI

openai_api_key = "EMPTY"
openai_api_base = "http://localhost:8000/v1"

client = OpenAI(
    api_key=openai_api_key,
    base_url=openai_api_base,
)

# Single-image input inference
image_url = "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg"

chat_response = client.chat.completions.create(
    model="microsoft/Phi-3.5-vision-instruct",
    messages=[{
        "role": "user",
        "content": [
            # NOTE: The prompt formatting with the image token `<image>` is not needed
            # since the prompt will be processed automatically by the API server.
            {"type": "text", "text": "What’s in this image?"},
            {"type": "image_url", "image_url": {"url": image_url}},
        ],
    }],
)
print("Chat completion output:", chat_response.choices[0].message.content)

# Multi-image input inference
image_url_duck = "https://upload.wikimedia.org/wikipedia/commons/d/da/2015_Kaczka_krzy%C5%BCowka_w_wodzie_%28samiec%29.jpg"
image_url_lion = "https://upload.wikimedia.org/wikipedia/commons/7/77/002_The_lion_king_Snyggve_in_the_Serengeti_National_Park_Photo_by_Giles_Laurent.jpg"

chat_response = client.chat.completions.create(
    model="microsoft/Phi-3.5-vision-instruct",
    messages=[{
        "role": "user",
        "content": [
            {"type": "text", "text": "What are the animals in these images?"},
            {"type": "image_url", "image_url": {"url": image_url_duck}},
            {"type": "image_url", "image_url": {"url": image_url_lion}},
        ],
    }],
)
print("Chat completion output:", chat_response.choices[0].message.content)
```

A full code example can be found in [examples/openai_chat_completion_client_for_multimodal.py](https://github.com/vllm-project/vllm/blob/main/examples/openai_chat_completion_client_for_multimodal.py).

```{tip}
Loading from local file paths is also supported on vLLM: You can specify the allowed local media path via `--allowed-local-media-path` when launching the API server/engine,
and pass the file path as `url` in the API request.
```

```{tip}
There is no need to place image placeholders in the text content of the API request - they are already represented by the image content.
In fact, you can place image placeholders in the middle of the text by interleaving text and image content.
```

````{note}
By default, the timeout for fetching images through HTTP URL is `5` seconds.
You can override this by setting the environment variable:

```console
$ export VLLM_IMAGE_FETCH_TIMEOUT=<timeout>
```
````

### Video

Instead of {code}`image_url`, you can pass a video file via {code}`video_url`.

You can use [these tests](https://github.com/vllm-project/vllm/blob/main/tests/entrypoints/openai/test_video.py) as reference.

````{note}
By default, the timeout for fetching videos through HTTP URL url is `30` seconds.
You can override this by setting the environment variable:

```console
$ export VLLM_VIDEO_FETCH_TIMEOUT=<timeout>
```
````

### Audio

Audio input is supported according to [OpenAI Audio API](https://platform.openai.com/docs/guides/audio?audio-generation-quickstart-example=audio-in).
Here is a simple example using Ultravox-v0.3.

First, launch the OpenAI-compatible server:

```bash
vllm serve fixie-ai/ultravox-v0_3
```

Then, you can use the OpenAI client as follows:

```python
import base64
import requests
from openai import OpenAI
from vllm.assets.audio import AudioAsset

def encode_base64_content_from_url(content_url: str) -> str:
    """Encode a content retrieved from a remote url to base64 format."""

    with requests.get(content_url) as response:
        response.raise_for_status()
        result = base64.b64encode(response.content).decode('utf-8')

    return result

openai_api_key = "EMPTY"
openai_api_base = "http://localhost:8000/v1"

client = OpenAI(
    api_key=openai_api_key,
    base_url=openai_api_base,
)

# Any format supported by librosa is supported
audio_url = AudioAsset("winning_call").url
audio_base64 = encode_base64_content_from_url(audio_url)

chat_completion_from_base64 = client.chat.completions.create(
    messages=[{
        "role": "user",
        "content": [
            {
                "type": "text",
                "text": "What's in this audio?"
            },
            {
                "type": "input_audio",
                "input_audio": {
                    "data": audio_base64,
                    "format": "wav"
                },
            },
        ],
    }],
    model=model,
    max_completion_tokens=64,
)

result = chat_completion_from_base64.choices[0].message.content
print("Chat completion output from input audio:", result)
```

Alternatively, you can pass {code}`audio_url`, which is the audio counterpart of {code}`image_url` for image input:

```python
chat_completion_from_url = client.chat.completions.create(
    messages=[{
        "role": "user",
        "content": [
            {
                "type": "text",
                "text": "What's in this audio?"
            },
            {
                "type": "audio_url",
                "audio_url": {
                    "url": audio_url
                },
            },
        ],
    }],
    model=model,
    max_completion_tokens=64,
)

result = chat_completion_from_url.choices[0].message.content
print("Chat completion output from audio url:", result)
```

A full code example can be found in [examples/openai_chat_completion_client_for_multimodal.py](https://github.com/vllm-project/vllm/blob/main/examples/openai_chat_completion_client_for_multimodal.py).

````{note}
By default, the timeout for fetching audios through HTTP URL is `10` seconds.
You can override this by setting the environment variable:

```console
$ export VLLM_AUDIO_FETCH_TIMEOUT=<timeout>
```
````

### Embedding

vLLM's Embeddings API is a superset of OpenAI's [Embeddings API](https://platform.openai.com/docs/api-reference/embeddings),
where a list of chat `messages` can be passed instead of batched `inputs`. This enables multi-modal inputs to be passed to embedding models.

```{tip}
The schema of `messages` is exactly the same as in Chat Completions API.
You can refer to the above tutorials for more details on how to pass each type of multi-modal data.
```

Usually, embedding models do not expect chat-based input, so we need to use a custom chat template to format the text and images.
Refer to the examples below for illustration.

Here is an end-to-end example using VLM2Vec. To serve the model:

```bash
vllm serve TIGER-Lab/VLM2Vec-Full --task embed \
  --trust-remote-code --max-model-len 4096 --chat-template examples/template_vlm2vec.jinja
```

```{important}
Since VLM2Vec has the same model architecture as Phi-3.5-Vision, we have to explicitly pass `--task embed`
to run this model in embedding mode instead of text generation mode.

The custom chat template is completely different from the original one for this model,
and can be found [here](https://github.com/vllm-project/vllm/blob/main/examples/template_vlm2vec.jinja).
```

Since the request schema is not defined by OpenAI client, we post a request to the server using the lower-level `requests` library:

```python
import requests

image_url = "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg"

response = requests.post(
    "http://localhost:8000/v1/embeddings",
    json={
        "model": "TIGER-Lab/VLM2Vec-Full",
        "messages": [{
            "role": "user",
            "content": [
                {"type": "image_url", "image_url": {"url": image_url}},
                {"type": "text", "text": "Represent the given image."},
            ],
        }],
        "encoding_format": "float",
    },
)
response.raise_for_status()
response_json = response.json()
print("Embedding output:", response_json["data"][0]["embedding"])
```

Below is another example, this time using the `MrLight/dse-qwen2-2b-mrl-v1` model.

```bash
vllm serve MrLight/dse-qwen2-2b-mrl-v1 --task embed \
  --trust-remote-code --max-model-len 8192 --chat-template examples/template_dse_qwen2_vl.jinja
```

```{important}
Like with VLM2Vec, we have to explicitly pass `--task embed`.

Additionally, `MrLight/dse-qwen2-2b-mrl-v1` requires an EOS token for embeddings, which is handled
by [this custom chat template](https://github.com/vllm-project/vllm/blob/main/examples/template_dse_qwen2_vl.jinja).
```

```{important}
Also important, `MrLight/dse-qwen2-2b-mrl-v1` requires a placeholder image of the minimum image size for text query embeddings. See the full code
example below for details.
```

A full code example can be found in [examples/openai_chat_embedding_client_for_multimodal.py](https://github.com/vllm-project/vllm/blob/main/examples/openai_chat_embedding_client_for_multimodal.py).